[VOL-1519]  Bug fix when deleting a device

Change-Id: I4e1f42d0c3f43e9778fd007b149f3711fb9f69f0
diff --git a/db/kvstore/etcdclient.go b/db/kvstore/etcdclient.go
index 1d2031d..42ab83c 100644
--- a/db/kvstore/etcdclient.go
+++ b/db/kvstore/etcdclient.go
@@ -407,6 +407,10 @@
 
 	channels, exists = c.watchedChannels.Load(key)
 
+	if channels == nil {
+		return nil, exists
+	}
+
 	return channels.([]map[chan *Event]v3Client.Watcher), exists
 }